This stone looked nearly the same, but it wasn't. It was the Amnesia Stone, which caused the wisher (and only the wisher) to forget that they had wished for anything and think that the new reality is normal.
Jessica walked towards the spot where she usually met up with her friends before school. And as she approached Lucy Corinth (her ditzy friend), she took out the stone, completely unaware that it wasn't the same stone she inherited from her grandfather.